Home | Contact ST  
Follow ST

Feature Article

Dual Gradient Drilling Technology At Work After Long Development Cycle
SEA CON Contributes Connectors, Cables to DGD Joint Industry Project


Michael Mulcahy

Face view of SEA CON's MSSK connector, which complies fully with API 16D design requirements.
SEA CON (El Cajon, California) began supporting proof-of-concept dual gradient drilling (DGD) projects well over a decade ago and has since collaborated with major oilfield contractors to supply more than 1,000 connectors and cable assemblies. It has also provided cable and connector logistical project management for the installation of a seagoing DGD system on the dynamically positioned deepwater drillship Pacific Santa Ana, currently operating in the Gulf of Mexico. The complexity of outfitting the entire system resulted in SEA CON's participation in planning, system integration and commissioning support at a much higher level than is customary for a connector and cable system manufacturer.

The relatively long history of DGD technology development from concept to first production drilling system illustrates that sometimes technical feasibility alone is not enough to ensure commercial success until the marketplace accepts it, and that process can be accelerated only so much.

In 1996, the Subsea MudLift Drilling Joint Industry Project (SMD-JIP) was formed to study the feasibility of an alternative deep-water drilling technology that came to be called dual gradient drilling. The technology's success hinged on development of a mud lift pump sufficiently robust to move drilling mud containing considerable embedded solids of various sizes to the surface, without clogging intermediate drilling system components.

Chevron North America Exploration and Production Co. (Houston, Texas) encapsulated the operating principle and benefits of DGD by saying: 'Unlike conventional deepwater drilling, which uses a single drilling fluid weight in the borehole, [DGD] employs two weights of drilling fluid'one above the seabed, the other below. This allows drillers to more closely match the pressures presented by nature and effectively eliminates water depth as a consideration in well design. DGD also allows drillers to more quickly detect and appropriately react to downhole pressure changes.'

In September 2001, the semisubmersible drillrig Ocean New Era, capable of drilling in 1,500-foot depths, drilled a successful DGD test well at 910 feet in the Gulf of Mexico, in the world's first subsea field test of a full-scale DGD system.

2008 Highlights
In 2008, a two-year, front-end engineering design (FEED) program was initiated for DGD. Due to the complex requirements for this project, SEA CON reached across multiple divisions, collaborating to provide connector design, project management, final assembly and testing services, ultimately delivering connectors and cables for the Pacific Santa Ana's major DGD components, including (from deepest to shallowest): blowout preventer (BOP), seawater-powered MaxLift pump, solids processing unit (SPU) to feed the MaxLift pump drilling mud containing solids at the maximum pumpable size of 1.5-inch thickness, and subsea rotating device (SRD) to separate mud from riser fluid. In total, SEA CON provided more than 360 cable assemblies, 720 bulkhead connector receptacles and multiple pressure-compensated distribution manifolds (totals including spares), most of which were purpose-developed to meet critical API guidelines. Pacific Santa Ana is rated for 12,000 feet of water during normal drilling operations. It is equipped with a DGD riser, a mud lift pump handling system, six mud pumps (three for drilling fluid and three for seawater), extensive fluid management system enhancements, and more than 13 miles of DGD-related cables. The DGD system is rated for 10,000 feet. To continue this article please click here.

Michael Mulcahy, president of Michael Mulcahy & Associates, Inc., is a former U.S. Navy officer and former Sea Technology magazine managing editor. He has written more than 100 ocean science and engineering articles. His interests include undersea connectors and cables, marine engineering, naval architecture, commercial diving, ROV operations, and ship salvage engineering. He is a graduate of the University of North Carolina at Chapel Hill. br />

Sea Technology is read worldwide in more than 110 countries by management, engineers, scientists and technical personnel working in industry, government and educational research institutions. Readers are involved with oceanographic research, fisheries management, offshore oil and gas exploration and production, undersea defense including antisubmarine warfare, ocean mining and commercial diving.